Test Stand with an Apparatus for Calibrating a Force-Measuring Device

ABSTRACT

A test stand encompasses a dynamometer, which is supported to oscillate about a main axis, from which a lever arm extends perpendicularly. For calibrating a force-measuring device, which is coupled to the lever arm, provision is made for a pneumatic cylinder as reference force-generating device. The reference force can be measured by a load cell and can be applied to the lever arm via a yoke. The force-measuring device, which is to be calibrated, the pneumatic cylinder, the load cell, and the yoke are disposed on the same side of the dynamometer and act on the same lever arm.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuing application, under 35 U.S.C. §120, of copendingInternational Application No. PCT/EP2010/002953, filed May 12, 2010,which designated the United States and was not published in English;this application also claims the priority, under 35 U.S.C. §119, ofGerman Patent Application No. 10 2009 035 410.7, filed Jul. 31, 2009;the prior applications are herewith incorporated by reference in theirentirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable

FIELD OF THE INVENTION

The invention relates to a calibrating method for a test stand as wellas to a test stand comprising an apparatus for calibrating aforce-measuring device.

BACKGROUND OF THE INVENTION

Such test stands, e.g., vehicle, engine or transmission test stands, areused by the automobile industry, among others, and support research anddevelopment with the help of functional tests, endurance trials for themechanical load test as well as consumption, exhaust gas, and noise orclimate analyses, for example. These test stands simulate the operationof a vehicle or of vehicle components under different environmental orapplication conditions. The vehicle or the vehicle components, which areto be tested, can be coupled on the test stand to a load device, e.g.,an asynchronous machine, a hydraulic dynamometer, or an eddy currentbrake. The load device simulates the load, against which the engine mustoperate in actual real operation.

In addition to numerous measured variables, the torque acting betweenthe vehicle and the load device is of particular importance. For thispurpose, the load device is supported to oscillate, so that the torque,which the vehicle applies to the load device, must be supported on thehousing of the load device, which is supported to oscillate. A leverarm, on the outer end of which provision is made for a force-measuringdevice (to measure the force that is transmitted via the lever arm), isattached to the housing of the load device. The torque, which acts onthe load device and which is thus output by the vehicle, can bedetermined in this manner by the measured force and the length of thelever arm, which is effective here.

Due to the fact that high demands are made on the accuracy of the torquemeasurement, the force-measuring device must be calibrated from time totime.

In the case of a roller-type test stand, the rollers must be freelyrotatable for calibrating. A certain reference torque, the value ofwhich is compared to the torque measured by the test specimen torquetransducer (lever arm and force-measuring device), is then applied tothe load device or to the housing of the load device, respectively, tocarry out an adjustment, in particular, of the force-measuring device,if necessary.

The reference torque must be predetermined or preselected, respectively,with the highest possible accuracy. A calibrating method, which is basedon the double lever principle, e.g., and which is described in EuropeanPatent Application 1,293,765, proved to be effective for this purpose.In this reference, provision is made on the housing of the load device(a dynamometer) for a lever arm, at the end of which the force-measuringdevice (which is to be calibrated) is disposed. Opposite the lever arm,a second lever arm must be attached to the housing of the load device onthe other side of the housing for carrying out the calibration,provision being made on the housing for a load device in the form of ahydraulic or a pneumatic cylinder. The cylinder applies a force to theadditional lever arm. The force is determined by a reference load cell.In the event that the load device is otherwise not loaded by any furtherexternal load, the actual force-measuring device must, accordingly,measure a corresponding value, which is a function of the lever ratios.If this is not the case, the force-measuring device must be adjusted.

In the case of the calibrating apparatuses known from the state of theart, a considerable additional technical effort, e.g., in the form ofadditional lever arms, is required in each case. In addition, it ispossible for the load device to be lifted out of its supports due tounsuitable force introduction, whereby the calibrating result can beimpacted or distorted, respectively.

SUMMARY OF THE INVENTION

The invention provides a test stand comprising an apparatus forcalibrating a force-measuring device that overcomes thehereinafore-mentioned disadvantages of the heretofore-known devices andmethods of this general type and that provide such features withminimized technical effort and, nonetheless, improved calibratingresults.

A test stand comprising an apparatus for calibrating a force-measuringdevice encompasses a load device, which is supported to oscillate abouta main axis, comprising a housing, from which a lever arm extendsperpendicular to the main axis. A force-transmission device is coupledto the lever arm for transmitting a force, which is orientedperpendicular to the main axis and perpendicular to the lever arm to oneside. A force-measuring device is coupled to the lever arm by theforce-transmission device. The test stand is characterized by areference force-generating device for generating a reference force, by areference force-measuring device, which is coupled to the referenceforce-generating device for measuring the respective generated referenceforce, and by a reference force-transmission device, which is coupled tothe lever arm, for transmitting the reference force to the lever arm.

The lever arm, thus, extends perpendicularly away from the housing in aknown manner. This does not necessarily imply that the lever arm mayonly extend away from the housing in perpendicular direction. Instead,this also implies that the lever arm extends away from the housingdiagonally, for example. What matters is only that the orientation ofthe lever arm comprises an extension component, which extendsperpendicularly away from the housing and the axis, to thus obtain alever arm, which is effective about the main axis.

The main axis of the load device corresponds to the main axis of thetest stand.

The lever arm is supported on the force-measuring device in the knownmanner via the force-transmission device, so that the force-measuringdevice can measure a force, which is exerted by the lever arm. In theevent that the location, at which the force-transmission device conveysthe force to the force-transmission device is known and thus also thedistance of this location from the main axis, the effective length ofthe lever arm is thus also known. The torque acting on the load devicecan be determined accurately from the effective length and the measuredforce.

Contrary to the state of the art, provision is additionally made on thelever arm, which is oriented only to one side, for the referenceforce-transmission device, which introduces the reference force, whichis generated by the reference-force generating device, on the lever arm.

The reference force-generating device thus generates the referenceforce, which is measured additionally by the reference force-measuringdevice, which is disposed in the flux of force. The reference force isintroduced on the lever arm so that the force is guided to theforce-measuring device at a different location via theforce-transmission device. The force-measuring device, e.g., a tensileforce-measuring device, can be calibrated in this manner such that it—inconsideration of the respective lever ratios—displays a forcemeasurement value, e.g., a tensile force measurement value, which isproportional to the reference force value measured by the referenceforce-measuring device.

The force-measuring device comprising the force-transmission device andthe reference force-generating device comprising the referenceforce-transmission device can be disposed on the same side of thehousing relative to the main axis. Through this, an additional lever armis not required for the calibrating process. Instead, the calibratingdevice (reference force-generating device, reference force-measuringdevice and reference force-transmission device) can be disposed in avicinity of the force-measuring device. In addition, a lifting of theload device out of its center of rotation or its supports, respectively,can be avoided.

The reference force-generating device can encompass a pneumatic orhydraulic cylinder unit. The reference force-generating device can,thereby, optionally generate forces in both directions. In this manner,the calibrating process can be simplified, accelerated, and automated.Different load cycles and steps can be realized simply, e.g., bynon-periodically controlling the reference force-generating device. Aremanence (zero point hysteresis) in the force-measuring chain, forexample, can thus also be detected and can be considered in response tothe adjustment. The measuring chain can be optimized in this manner.

The load device can be a dynamometer, wherein the lever arm is fastenedto a stator housing of the dynamometer and extends perpendicular to themain axis. In practice, a dynamometer has proved to be highly effectiveas load device. The lever arm can also extend diagonally to the statorhousing. What matters is only that it encompasses an extensioncomponent, which runs perpendicular to the main axis and thus to thestator housing.

The reference force-transmission device can be disposed at the outer endof the lever arm. In this manner, the length of the lever arm isutilized fully and the accuracy of the calibration is improved. Theforce-transmission device, which is necessary for the normal measuringoperation, e.g., a tensile force-transmission device, and theforce-measuring device can then be disposed between the outer end of thelever arm and the stator housing of the load device.

In one exemplary embodiment, the reference force-transmission deviceencompasses a yoke, which encloses the outer end of the lever arm. Areliable transmission of the reference force is possible with the helpof the yoke. In addition, the provision of the yoke allows for a highlyaccurate determination of the effective length of the lever arm and thusof the measuring accuracy.

For transmitting the reference force, a pairing of a knife edge and aknife edge support can be disposed above and below the lever armrespectively between the yoke and the lever arm. Either the knife edgecan thereby respectively be provided on the lever arm and the oppositeknife edge support can be provided on the yoke or the knife edge canrespectively be provided on the yoke and the opposite knife edge supportcan be provided on the lever arm. It can be ensured, with the help ofthe knife edge and the assigned knife edge support between yoke andlever arm, that the reference force is transmitted onto the lever armonly via the knife edge, thus with a line contact. The knife edgethereby extends parallel to the main axis. The effective length of thelever arm can be determined in a correspondingly accurate manner.

The yoke can encompass a substantially square frame, which encloses theouter end of the lever arm. The designation of a “square” frame does notrequire that the frame must actually encompass exactly four corners.Instead, a square frame is to be understood as a frame, whichencompasses an upper side and a lower side, which are connected to oneanother by two lateral connecting elements. On principle, this resultsin a type of square (or rectangle), which can, of course, also encompassmore corners or rounded corners.

In an alternative exemplary embodiment, a flange of a piece of foil canbe fastened respectively to the frame on the upper side and/or on thelower side of the frame, wherein an area of the piece of foil, which islocated between the upper side and the lower side of the frame, isfastened to the end of the lever arm. In this alternative, it is notnecessary to provide the above-described pairings of knife edge andknife edge support. Instead, the reference force is transmitted via thepiece of foil. The piece of foil can be plastic or metal. It encompassesa high tensile strength, but a minimal stiffness. Accordingly, the pieceof foil is suitable for transmitting the reference force as tensileforce from the yoke to the lever arm. However, in the event that theforce acts in the opposite direction, a compressive force, which cannotbe transmitted due to the low stiffness or compressive strength,respectively, will now be applied to the part of the piece of foil,which was previously tensioned. The stiffness should thereby be as lowas possible, so as not to impact the reference force. Vice versa, thereference force is then transmitted by the other, opposite part of thepiece of foil, which is then able to convey a tensile force.

In response to the installation of the piece of foil, the foil can beinstalled loosely, e.g., with a slight bulge or corrugation, thus in anyevent without initial tension, to ensure a mechanically unloaded statein or around the zero point.

The piece of foil should be as thin as possible, so as to be able toaccurately determine the effective length of the lever arm.

The piece of foil can be embodied as a one-piece piece of foil. In thiscase, the piece of foil can be clamped with its upper flange to theupper side of the frame of the yoke and with its lower flange on thelower side of the yoke frame. A middle area of the piece of foil canthen be clamped to a frontal end of the lever arm.

In another exemplary embodiment, the piece of foil can be formed by twoseparate pieces of foil, wherein the one of the pieces of foil is anupper piece of foil, which is clamped between the upper flange of theframe and the frontal end of the lever arm, and the other one of thepieces of foil is a lower piece of foil, which is clamped between thelower flange of the frame and the frontal end of the lever arm.

The decision whether the piece of foil is realized as one part or in theform of two separate pieces of foil will substantially have to be madebased upon assembly considerations.

The reference force-generating device can be supported on a support,which is coupled to a base of the test stand, via a compensating device,wherein the compensating device is embodied for compensating alignmentand/or angle errors. With the help of the compensating device, theposition and orientation of the reference force-generating device can beadjusted with high accuracy, to generate a reference force, which actsexactly perpendicular on the lever arm.

In one exemplary embodiment, provision can be made for a control devicefor controlling the reference force-generating device, wherein a higherforce than the nominal reference force can be effected temporarily bythe control device in response to the adjustment of a desired nominalreference force when the reference force is increased or a lower forcethan the nominal reference force can be effected temporarily when thereference force is reduced.

An overshooting when generating the reference force can be effected withthis measure, e.g., to overcome the static friction in the supports ofthe load device. The control device effects a temporary overshootingbeyond the actually desired nominal reference force value and onlyadjusts the desired reference force after the overshooting.

In a method for calibrating a force-measuring device in a test stand ofthe invention, provision is initially made for a test stand comprisingthe above-specified features. This is followed by the steps of:

-   -   generating a reference force by the reference force-generating        device;    -   measuring the reference force by the reference force-measuring        device;    -   measuring the force acting on the force-measuring device in the        form of an actual force value;    -   determining a nominal force value, which would have to apply to        the force-measuring device due to the measured reference force        and the effective lever ratios; and    -   calibrating the force-measuring device such that the actual        force value measured by the force-measuring device, is compared        to the nominal force value.

After the calibration, an adjustment of the force-measuring deviceand/or of the electronic circuits, which are connected thereto, can becarried out, if necessary.

The method is suitable, in particular, for calibrating a tensileforce-measuring device and can be embodied such that an overshooting ofthe reference force beyond the desired (target) reference force value isinitially effected when generating the reference force.

The reference force-generating device can be controlled such that thelever arm is not loaded with a force from the reference force-generatingdevice. A mechanically unloaded state of the lever arm can be obtainedthrough this, to calibrate the zero point.

Although the invention is illustrated and described herein as embodiedin a test stand comprising an apparatus for calibrating aforce-measuring device, it is, nevertheless, not intended to be limitedto the details shown because various modifications and structuralchanges may be made therein without departing from the spirit of theinvention and within the scope and range of equivalents of the claims.Additionally, well-known elements of exemplary embodiments of theinvention will not be described in detail or will be omitted so as notto obscure the relevant details of the invention.

Additional advantages and other features characteristic of the presentinvention will be set forth in the detailed description that follows andmay be apparent from the detailed description or may be learned bypractice of exemplary embodiments of the invention. Still otheradvantages of the invention may be realized by any of theinstrumentalities, methods, or combinations particularly pointed out inthe claims.

Other features that are considered as characteristic for the inventionare set forth in the appended claims. As required, detailed embodimentsof the present invention are disclosed herein; however, it is to beunderstood that the disclosed embodiments are merely exemplary of theinvention, which can be embodied in various forms. Therefore, specificstructural and functional details disclosed herein are not to beinterpreted as limiting, but merely as a basis for the claims and as arepresentative basis for teaching one of ordinary skill in the art tovariously employ the present invention in virtually any appropriatelydetailed structure. Further, the terms and phrases used herein are notintended to be limiting; but rather, to provide an understandabledescription of the invention. While the specification concludes withclaims defining the features of the invention that are regarded asnovel, it is believed that the invention will be better understood froma consideration of the following description in conjunction with thedrawing figures, in which like reference numerals are carried forward.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying figures, where like reference numerals refer toidentical or functionally similar elements throughout the separateviews, which are not true to scale, and which, together with thedetailed description below, are incorporated in and form part of thespecification, serve to illustrate further various embodiments and toexplain various principles and advantages all in accordance with thepresent invention. Advantages of embodiments of the present inventionwill be apparent from the following detailed description of theexemplary embodiments thereof, which description should be considered inconjunction with the accompanying drawings in which:

FIG. 1 is a fragmentary, perspective view of a section of an exemplaryembodiment of a test stand according to the invention including acalibrating device;

FIG. 2 a fragmentary, perspective view of an image section of the teststand of FIG. 1;

FIG. 3 a fragmentary, and partially cross-sectional view of a schematicillustration comprising one end of a lever arm and a yoke enclosing thelever arm according to the invention;

FIG. 4 is a perspective view of an alternative exemplary embodiment of acalibrating device according to the invention;

FIG. 5 is a cross-sectional view of the calibrating device of FIG. 4;and

FIG. 6 is a perspective view of a further alternative exemplaryembodiment of a calibrating device according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

As required, detailed embodiments of the present invention are disclosedherein; however, it is to be understood that the disclosed embodimentsare merely exemplary of the invention, which can be embodied in variousforms. Therefore, specific structural and functional details disclosedherein are not to be interpreted as limiting, but merely as a basis forthe claims and as a representative basis for teaching one skilled in theart to variously employ the present invention in virtually anyappropriately detailed structure. Further, the terms and phrases usedherein are not intended to be limiting; but rather, to provide anunderstandable description of the invention. While the specificationconcludes with claims defining the features of the invention that areregarded as novel, it is believed that the invention will be betterunderstood from a consideration of the following description inconjunction with the drawing figures, in which like reference numeralsare carried forward.

Alternate embodiments may be devised without departing from the spiritor the scope of the invention. Additionally, well-known elements ofexemplary embodiments of the invention will not be described in detailor will be omitted so as not to obscure the relevant details of theinvention.

Before the present invention is disclosed and described, it is to beunderstood that the terminology used herein is for describing particularembodiments only and is not intended to be limiting. The terms “a” or“an”, as used herein, are defined as one or more than one. The term“plurality,” as used herein, is defined as two or more than two. Theterm “another,” as used herein, is defined as at least a second or more.The terms “including” and/or “having,” as used herein, are defined ascomprising (i.e., open language). The term “coupled,” as used herein, isdefined as connected, although not necessarily directly, and notnecessarily mechanically.

Relational terms such as first and second, top and bottom, and the likemay be used solely to distinguish one entity or action from anotherentity or action without necessarily requiring or implying any actualsuch relationship or order between such entities or actions. The terms“comprises,” “comprising,” or any other variation thereof are intendedto cover a non-exclusive inclusion, such that a process, method,article, or apparatus that comprises a list of elements does not includeonly those elements but may include other elements not expressly listedor inherent to such process, method, article, or apparatus. An elementproceeded by “comprises . . . a” does not, without more constraints,preclude the existence of additional identical elements in the process,method, article, or apparatus that comprises the element.

As used herein, the term “about” or “approximately” applies to allnumeric values, whether or not explicitly indicated. These termsgenerally refer to a range of numbers that one of skill in the art wouldconsider equivalent to the recited values (i.e., having the samefunction or result). In many instances these terms may include numbersthat are rounded to the nearest significant figure.

Herein various embodiments of the present invention are described. Inmany of the different embodiments, features are similar. Therefore, toavoid redundancy, repetitive description of these similar features maynot be made in some circumstances. It shall be understood, however, thatdescription of a first-appearing feature applies to the later describedsimilar feature and each respective description, therefore, is to beincorporated therein without such repetition.

Described now are exemplary embodiments of the present invention.Referring now to the figures of the drawings in detail and first,particularly to FIGS. 1 and 2, there is shown a first exemplaryembodiment of a section of a test stand according to the invention. Thetest stand encompasses a base frame 1, which is configured in a verymassive and stable manner, comprising a plurality of steel beams orpipes, respectively. The base frame 1 encompasses a support frame 1 a,on which a dynamometer 2 as a load device is supported to oscillateabout its main axis X. The oscillating support cannot be seen in FIG. 1,but is well known from the state of the art. For instance, it is commonto support a dynamometer so that it can oscillate and thus determinetorque acting on the dynamometer by the reaction force on a lever arm,which is attached to the dynamometer.

In the instant case, a lever arm 3, which extends perpendicular to themain axis X away from the stator housing, is also attached to the statorhousing of the dynamometer 2.

The lever arm 3 is embodied to be so stiff that it deforms as little aspossible even in response to a load. A force sensor 4 in the form of anS-shaped bending arm as force-measuring device is disposed approximatelyin the center of the lever arm 3 below the lever arm 3. The force sensor4 is placed between an upper spring bar 5 and a lower spring bar 6. Theupper spring bar 5 serves as force-transmission device and connects theforce sensor 4 to the lever arm 3, while the lower spring bar 6 supportsthe force sensor 4 against the base 1.

With the help of the force sensor 4, a force with which the lever arm 3is supported on the upper spring bar 5, can be determined accuratelyduring the normal test operation. With the help of the measured forceand by the effective length of the lever arm 3 (measured from the mainaxis X to the location, at which the upper spring bar 5 is coupled tothe lever arm 3), the torque, which acts on the dynamometer 2 by thenon-illustrated test specimen (e.g., a vehicle engine), can bedetermined.

The force-measuring chain comprising the force sensor 4 must becalibrated from time to time. For this purpose, provision is made for acalibrating apparatus, which encompasses a pneumatic cylinder 7 asreference force-generating device, a load cell 8 (e.g., a ring torsionload cell) as reference force-measuring device and a referenceforce-transmission device 9 for introducing the reference force onto thelever arm 3.

With the help of the calibrating apparatus, an accurately determinedreference force can be exerted on the lever arm 3. A corresponding forcemust, accordingly, act on the force sensor 4 as a function of the leverarm ratios. In the event that the force sensor 4 does not measure thisforce, but a differing measuring value, it can be adjusted in a simplemanner. The dynamometer 2 is unloaded during the calibrating process andis separated from the test specimen, so that the reference torque mustbe supported completely by the force sensor 4 in the ideal case.

The pneumatic cylinder 7 is suited to adjust a predetermined force withhigh accuracy and to keep it stable. It is advantageous when thepneumatic cylinder 7 acts in both directions, thus upward and downward,and when it can generate corresponding forces.

The load cell 8 serves to measure the reference force generated by thepneumatic cylinder 7, which is introduced into the lever arm 3 via thereference force-transmission device 9.

The load cell 8 can also be realized by different components, e.g., byan S-shaped bending arm. Likewise, the force sensor 4 can also berealized by a different component, e.g., by a load cell.

The reference force-transmission device 9 is embodied in the form of ayoke 10, which encompasses a substantially square frame, which enclosesone end of the lever arm 3.

FIG. 3 shows the setup of the yoke 10 in relation to the end of thelever arm 3 in a basic illustration. At the end of the lever arm 3, aknife edge 11 is respectively disposed on the upper and lower sides.Knife edge supports 12 are embodied in the yoke 10 opposite the twoknife edges 11. The knife edge supports 12 are illustrated in FIG. 3with a prism-shaped depression. However, they can also be formed by flatsmall hard metal plates or in a different manner, for example, to ensurean accurate transmission of the respective force in cooperation with theknife edges 11.

In response to a vertical displacement of the yoke 10 due to an affectcaused by the pneumatic cylinder 7, one of the knife edge supports 12moves across the knife edge 11 associated with the respective knife edgesupport 12. This creates a line contact, which extends perpendicular tothe drawing plane in FIG. 3, along the knife edge 11. The knife edge 11extends along the main direction X of the dynamometer 2.

The force generated by the pneumatic cylinder 7 is transferred to thelever arm 3 via the line contact, whereby the lever arm 3 attempts topivot the dynamometer 2 in its oscillating support. Accordingly, aforce, which can be measured by the force sensor 4, is introduced at theforce sensor 4.

In response to a movement of the yoke 10 in an opposite direction due toan opposite affect of the pneumatic cylinder 7, the pairing of knifeedge 11 and knife edge support 12 located opposite one another comesinto contact. The lever arm 3 is, then, loaded in the oppositedirection.

FIGS. 4 and 5 (which are sectional illustrations) show an alternative,in particular, for the yoke 10. The yoke 10 is thereby also embodied asa square frame 13. However, it does not encompass knife blades—as doesthe alternative illustrated in FIG. 3. Instead, the yoke 10 or the frame13, respectively, comprises two planar halves 13 a and 13 b, which areheld together by screws, for example.

A resiliently flexible, tensile metal foil 14 is inserted between thetwo halves 13 a and 13 b. Provided that it encompasses a sufficientstrength, a plastic foil can also be used instead of the metal foil 14.

On the opposite sides, the metal foil 14 is clamped on the top and onthe bottom between the halves 13 a and 13 b by a screw connection, forexample. In the middle area, the metal foil 14 is fastened to the frontside of the lever arm 3, whereby the yoke 10 is held on the lever arm 3.The fastening of the yoke 10 to the lever arm 3 is formed by a foilscrew connection, wherein a clamping piece 15, which is attached to themetal foil 14, connects the metal foil 14 to the front side of the leverarm 3.

The effective length (length, which is important for the determinationof the reference torque resulting from the effective reference force) ofthe lever arm 3 cannot change with this type of fastening of the metalfoil 14 to the lever arm 3 or with this type of force introduction intothe lever arm 3, respectively, as it is possible in the case of theembodiment shown in FIG. 3 due to transverse force effects. In the caseof the type of force transmission in the yoke shown in FIGS. 4 and 5,the foil half (upper foil half 14 a or lower foil half 14 b) that istensioned always participates in the force-transmission. In the eventthat the pneumatic cylinder 7 generates a tensile force downward, thelower foil half 14 b transmits the tensile force to the lever arm 3; inthe event that the pneumatic cylinder 7 generates a compressive forceupward, the upper foil half 14 a transmits the force of the pneumaticcylinder 7, which is oriented upward, in the yoke 10.

The effective length of the lever arm 3, which is included in the torquecomputation, is comprised of the horizontal lever arm length (distancefrom the main axis X to the force-introduction location) plus half ofthe foil thickness. This length needs to be determined accurately onlyonce, it does not change, because wear cannot occur.

A compensating device 16 is shown in the lower figure part of FIG. 4,but also in FIGS. 1 and 2. The compensating device 16 couples thepneumatic cylinder 7 to the base 1 of the test stand to support thepneumatic cylinder 7. The compensating device 16 is, thereby, able tocompensate alignment and/or angle errors. For this purpose, thecompensating device 16 encompasses a lower plate 17 and an upper plate18, which are coupled to one another by screw connections, for example.By adjusting the screws, the mentioned errors can be compensated.

FIG. 6 shows an alternative, in which provision is made for a ball joint19 instead of the compensating device 16. The ball joint 19 alsoprovides for the compensation of alignment or angle errors.

The foregoing description and accompanying drawings illustrate theprinciples, exemplary embodiments, and modes of operation of theinvention. However, the invention should not be construed as beinglimited to the particular embodiments discussed above. Additionalvariations of the embodiments discussed above will be appreciated bythose skilled in the art and the above-described embodiments should beregarded as illustrative rather than restrictive. Accordingly, it shouldbe appreciated that variations to those embodiments can be made by thoseskilled in the art without departing from the scope of the invention asdefined by the following claims.

1. A force-measuring calibration test stand, comprising a load device:comprising a housing and a main axis; being supported at the housing;and being operable to oscillate about the main axis; a lever armextending away from the housing perpendicular to the main axis; aforce-transmission device coupled to the lever arm and operable totransmit a force oriented perpendicular to the main axis andperpendicular to the lever arm; a force-measuring device coupled to thelever arm by the force-transmission device; and a force-measuringcalibration device comprising: a reference force-generating deviceoperable to generate a reference force; a reference force-measuringdevice coupled to the reference force-generating device and operable tomeasure the reference force generated; and a referenceforce-transmission device coupled to the lever arm and operable totransmit the reference force to the lever arm.
 2. The test standaccording to claim 1, wherein the force-measuring device, theforce-transmission device, the reference force-generating device, andthe reference force-transmission device are on the same side of thehousing relative to the main axis.
 3. The test stand according to claim1, wherein the reference force-generating device comprises one of apneumatic cylinder unit and a hydraulic cylinder unit.
 4. The test standaccording to claim 1, wherein: the load device is a dynamometer having astator housing; and the lever arm is fastened to the stator housing andextends perpendicular to the main axis.
 5. The test stand according toclaim 1, wherein: the lever arm has an outer end; and the referenceforce-transmission device is at the outer end of the lever arm.
 6. Thetest stand according to claim 1, wherein: the lever arm has an outerend; and the reference force-transmission device comprises a yokeenclosing the outer end of the lever arm.
 7. The test stand according toclaim 6, wherein: transfer pairs each comprising a knife edge and aknife edge support are respectively disposed above and below the leverarm between the yoke and the lever arm and are operable to transfer thereference force; and one of: the knife edge of each transfer pair isprovided on the lever arm and the opposing knife edge support isprovided on the yoke; and the knife edge of each transfer pair isprovided on the yoke and the opposing knife edge support is provided onthe lever arm.
 8. The test stand according to claim 6, wherein: the yokecomprises a rectangular frame enclosing the outer end of the lever arm;a flange of a piece of foil is fastened respectively to the frame on atleast one of the upper side of the frame and the lower side of theframe; and an area of the piece of foil located between the upper andlower sides of the frame is fastened to the outer end of the lever arm.9. The test stand according to claim 8, wherein: the lever arm has afrontal end; and the piece of foil has: an upper flange clamped to theupper side of the frame; a lower flange clamped to the lower side of theframe; and a middle area clamped to the frontal end of the lever arm.10. The test stand according to claim 8, wherein: the frame has upperflange and a lower flange; the lever arm has a frontal end; the piece offoil is formed by two separate pieces of foil; one of the pieces of foilis an upper piece of foil clamped between the upper flange of the frameand the frontal end of the lever arm; and the other one of the pieces offoil is a lower piece of foil clamped between the lower flange of theframe and the frontal end of the lever arm.
 11. The test stand accordingto claim 1, further comprising: a test stand base; a support comprisinga compensating device, being coupled to the test stand base, andsupporting the reference force-generating device; and the compensatingdevice being operable to compensate for at least one of alignment errorsand angle errors.
 12. The test stand according to claim 1, furthercomprising a control device operable: to control the referenceforce-generating device; and to effect one of: a force higher than anominal reference force temporarily in response to an adjustment of adesired nominal reference force when the reference force is increased;and a lower force than the nominal reference force temporarily inresponse to an adjustment of a desired nominal reference force when thereference force is reduced.
 13. The test stand according to claim 5,wherein the reference force-transmission device comprises a yoke. 14.The test stand according to claim 13, wherein the yoke encloses theouter end of the lever arm.
 15. A method for calibrating aforce-measuring device in a test stand, which comprises: providing atest stand comprising: a load device supported to oscillate about a mainaxis, the load device having a housing; a lever arm extendingperpendicular to the housing of the load device; the force-measuringdevice coupled to the lever arm; a reference force-generating devicedisposed the same side of the housing as the force-measuring device andcoupled to the lever arm; and a reference force-measuring devicedisposed in a flux of force between the reference force-generatingdevice and the lever arm and operable to measure a reference forcegenerated; generating the reference force with the referenceforce-generating device; measuring the reference force with thereference force-measuring device; measuring a force acting on theforce-measuring device in the form of an actual force value; determininga nominal force value that would have to apply to the force-measuringdevice due to a measured reference force and effective lever ratios; andcalibrating the force-measuring device by comparing the actual forcevalue measured by the force-measuring device with the nominal forcevalue.
 16. The method according to claim 15, which further comprisesinitially effecting an overshoot of the reference force beyond a desiredreference force value when generating the reference force.
 17. Themethod according to claim 15, which further comprises controlling thereference force-generating device so that the lever arm is not loadedwith a force from the reference force-generating device.